The present invention relates to cis-oxalato (trans-1-1,2-cyclohexanediamine) Pt(II) of optically high purity which can be employed as raw material of a carcinostatic agent.
While a platinum (II) complex of 1,2-cyclohexanediamine as a platinum (II) complex exhibiting a carcinostatic activity is known, the complex is a mixture of isomers synthesized from a mixture of isomers (cis, trans-d and trans-l) existing in 1,2-cyclohexanediamine the starting material thereof.
The trans and cis isomers of the 1,2 cyclohexanediamine may be optically resoluted by means of a metal complex utilizing the difference of solubilities between the two isomers. For example, in Japanese patent publication No. 60-41077, while the cis-isomer is precipitated by adding a nickel (II) salt to such a nonaqueous solvent such pure methanol containing the two isomers, the trans-isomer is precipitated by adding the nickel salt and hydrochloric acid and aqueous sodium hydroxide. Since the trans-isomer of the nickel complex is slightly soluble in water and easily soluble in an organic solvent and the cis-isomer is slightly soluble in an organic solvent and easily soluble in water, the optical resolution can be conducted.
Although cis-oxalato (trans-1-1,2-cyclohexanediamine) Pt(II) was synthetically obtained through a reaction between the trans-1-1,2-cyclohexanediamine obtained in accordance with the above method and K.sub.2 PtCl.sub.1 (Japanese patent publication No. 60-41077). This was also found to be the mixture with cis-oxalato (trans-d-1,2-cyclohexanediamine) Pt(II). No data are presented in the Japanese patent publication No. 60-41077 which confirm the optical purity of the cis-oxalato (trans-1-1,2-cyclohexanediamine) Pt(II) and relate to circular duchroism (CD) exhibiting its steric configuration and to an angle of rotation ([.alpha.].sub.D) exhibiting its optical activity. No differences can be distinguished between their respective elemental analysis values, infrared spectra and electron spectra of the isomers mentioned in the Japanese patent publication No. 60-41077.
In the cis-oxalate (trans-1-1,2-cyclohexanediamine) Pt(II) conventionally reported, the isolation of the complex consisting of two trans-dl isomers is insufficient so that the question of the purity of the isolated Pt(II) complex remains.
Large differences in connection with a carcinostatic activity and a secondary effect between isomers of many optically active medicines, and their optical purity is especially important when they are employed as medicines.